1. Field of the Invention
The present invention relates to a process for production of sulfonium compounds and novel methylthiophenol derivatives. More particularly, it is concerned with a process for producing sulfonium compounds, p-dialkylsulfoniophenol derivatives represented by the general formula (III), by sulfoniumating alkylthiophenol deratives represented by the general formula (I) with dialkyl sulfate represented by the general formula (II).
General Formula (I): ##STR3## General Formula (II): (R.sup.2 )SO.sub.4 General Formula (III): ##STR4##
In the general formulas (I), (II) and (III), R.sup.1 and R.sup.2 may be identical or different and are each a lower alkyl group having 1 to 4 carbon atoms, and X is a hydrogen atom, a halogen atom, or a lower alkyl group having 1 to 4 carbon atoms. In the general formulas (I) and (III), R is an allyloxy group, a 9-fluorenylmethoxy group, a 2,2,2-trichloroethoxy group, or a 2-chlorobenzyloxy group.
Sulfonium compounds represented by the general formula (III) are useful compounds as reagents for introduction of an acyl group as a protecting group to various compounds in the organic chemical field, e.g., synthesis of peptides, because they exhibit acylating action in an aqueous solution.
The term "acyl" as used herein refers to a group as derived by removal of a hydroxyl group from a carbonic acid monoester.
The present invention further relates to novel methylthiphenol derivatives capable of being precursors for the above sulfonium compounds and more specifically to novel methylthiophenol derivatives represented by the general formula (I'). ##STR5## wherein R is the same as defined above.
2. Description of the Related Arts
For the production of the sulfonium compounds represented by the general formula (III), a method of reacting acid halides, i.e., carbonylhalogenide compounds with p-dialkylsulfoniophenol alkylsulfate in the presence of a base has been generally employed.
Japanese Patent Application Laid-Open No. 8365/1988, for example, discloses a method in which acid chloride is used as the acid halide, and triethylamine is used as the base.
This method, however, is not necessarily satisfactory for practical use, because a complicated operation is required for separation and purification of the objective products, sulfonium compounds of the general formula (III), from by-products of triethylamine hydrochloride.
For example, when p-dimethylsulfoniophenol methylsulfate and 9-fluorenylmethoxycarbonyl chloride are reacted in the presence of triethylamine, the yield of the objective 9-fluorenylmethyl p-dimethylsulfoniophenyl carbonate methylsulfate is about 40%, and its purity is as low as 80 to 85%.
The present invention is intended to provide an industrially advantageous process for producing the desired sulfonium compounds with high efficiency and at low production costs by reacting alkylthiophenol derivatives and dialkyl sulfate.
The present inventors made investigations on a method of synthesis of sulfonium compounds represented by the general formula (III) in order to overcome the above problems. As a result, it has been found that the objective sulfonium compounds can be produced with high efficiency, substantially without any complicated purification operations, by reacting alkylthiophenol derivatives represented by the general formula (I) and dialkyl sulfate represented by the general formula (II).
Moreover, in the course of the above investigations, it has been found that specified compounds of the alkylthiophenol derivatives represented by the general formula (I) to be used as the starting material in the above reaction are novel compounds.
Based on the findings, the present invention has been accomplished.